Biel, dressed in a navy tank top and white pants, had a blast rocking out in the VIP mezzanine area during the show, which was sponsored by MasterCard. "She knew all the words to his songs and was dancing the whole time," an onlooker tells PEOPLE. "She looked very proud."

Biel also occasionally chatted with Sudeikis and fiancée Wilde, who were seated at the next table with Samberg and fiancée Newsom and sipped on water throughout the show.

"Jason and Olivia were so cute and affectionate," adds the onlooker. "He was whispering into her ear during the concert. They looked very much in love."

Perhaps no one had as much fun as Thurman and Shields, who were also seated next to each other in the VIP area.

Thurman, who brought daughter Maya Ray, "was freaking out, singing and dancing with Maya and having so much fun with her," the onlooker says." At one point, the actress, dressed in a white tank top and jeans, took a break from dancing and singing to snap cell phone pictures with Shields, who was with a female companion. "They were having so much fun," says the observer.

Saw our buddy @jtimberlake bring sexy back to NYC tonight.A young lady through her panties at him by accident. Hope she's not cold! #JTFun